Does the Prius Prime ICE always start?

Discussion in 'Prime Technical Discussion' started by kevin.c, Feb 9, 2019.

  1. kevin.c

    kevin.c Member

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    Does this do regen on the prius prime? On my normal prius, it just connects the wheels to the ICE.
     
  2. Tideland Prius

    Tideland Prius Moderator of the North
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    In EV mode, yes. In HV mode, no.*


    *except below 20mph. This feature was removed from the Gen 4 and the Gen 4 always engages the engine but the Prime acts like older Prii.
     
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  3. Zed Ruhlen

    Zed Ruhlen Member

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    There isn't an option to not fully charge. I put it on the charger and leave it. Using the HVAC before the hill is enough to drain it so that it isn't fully charged when I hit the hill.

    The engine isn't consuming electricity but rather running at a reduced rate to create drag on the motor/generator which feeds electricity back to the main motor at a net loss of energy. Even when you stop it still runs, probably to heat up.
     
  4. Bill Norton

    Bill Norton Senior Member

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    If you are charging L1 you could use a simple timer between the L1 and the wall socket.

    Your solution wastes electrical energy and your own energy fussing with this work around on a daily basis.

    Other/better PHEV's have built in charging timer functions. It's just SW after all....
    Oh well. Whatever you like. It's probably not a lot of wasted dollars doing it your way....
     
  5. jb in NE

    jb in NE Senior Member

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    The Prime has a charging timer function. If a full charge is not desired at start of drive, set the timer for completion an hour after your leave time.

    Yes, but in EV mode with sufficient ability of battery to absorb the charge. If battery is full, then no effect. If I know a big downhill is ahead and I am in HV mode, I may need to switch to EV mode to discharge the battery a bit early to make space.

    If in HV mode and sufficient battery capacity to absorb, the car will go into EV and charge the battery.
     
    #25 jb in NE, Apr 18, 2019
    Last edited by a moderator: Apr 18, 2019
  6. jerrymildred

    jerrymildred Senior Member

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    I was going to say the same thing. In fact, I did the same thing this morning.
     
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  7. Zed Ruhlen

    Zed Ruhlen Member

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    Exactly how would a timer help? I don't know the amount of time it's going to take to charge to say 90% of a full charge. And to the other commenters, this is more convoluted than just running the HVAC on my way to the hill. It would be great if Toyota gave me the option to charge to 90% (after all it IS just software) but they don't.

    A timer is the most Kludgy method imaginable for dealing with this issue. Of course the most elegant solution would be to just use the mechanical brakes when the battery is fully charged. It's not likely to be a common condition and would add minimal wear to the brakes over the life of the car.
     
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  8. kevin.c

    kevin.c Member

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    I think the Prius brakes are smaller than what would be required for a car of its weight. So it really needs regen (whether to battery or to MG1 to spin the engine).
     
  9. jerrymildred

    jerrymildred Senior Member

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    That would be really dangerous. A hard stop (panic stop, if you will) is 100% friction braking. I can't begin to count the number of times traffic in Tampa has forced me to stop from 60 mph so hard that I show no regeneration at all. There is only one thing that a car has to absolutely be able to do and that is to stop once it's moving.
     
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  10. Zed Ruhlen

    Zed Ruhlen Member

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    Actually the opposite is true. Prius brakes are bigger because the car is heavier than similar sized cars. As mentioned above brakes are required to stop the car rapidly. The regen isn't nearly strong enough to stop the car
     
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  11. fuzzy1

    fuzzy1 Senior Member

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    Overheated brakes on long hill descents used to be common on cars, and still happens on trucks. That is one reason why a choice for engine braking is mandatory.
    What Jerry said, for single highway speed stops, where regular Prius regen can provide only about 5% of the required stopping power, so full friction braking capacity is still needed.

    Then add in long steep mountain descents where a regular Prius battery fills up in the first few hundred vertical feet, or a plug-in Prius battery might start already full. Even regular friction brakes cannot handle 3000 - 5000 feet of steep descent, so require engine braking assist. Downsized friction brakes would be disastrous.
     
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  12. kevin.c

    kevin.c Member

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    Guess i shouldn't believe everything I read on the Internet :)
     
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  13. fuzzy1

    fuzzy1 Senior Member

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    You may have read that the majority of regular braking is done with regen, so that the brake pads last much longer than on non-hybrids. This is generally true, but depends strongly on conditions and driver style. Regen can readily handle the majority of braking in city traffic if the driver is being efficient, doing mostly light to moderate braking with plenty of time and braking distance available.

    But some drivers simply do braking inefficiently, going harder over shorter distances at the last moment, defeating regen. And everyone encounters at least some unanticipated situations demanding harder braking, far beyond regen's capacity. The car's friction-only brakes must still be able to handle this.

    Then there is highway speed emergency braking. A regular car's friction brakes can perform a 60-to-zero stop in about 120 feet. A fully loaded Prius trying to stop on regen-only will go over 1000 feet even if the driver is perfect at adjusting braking force on the fly to the maximum possible regen level, which changes with speed. Without that perfect continual adjustment, expect closer to 2000 feet.

    Thus, even with regen covering most normal braking use, the Prius still needs full-performance friction brakes for the less frequent but critical emergency needs.
     
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